The bleaching of fatty acids often is done with clay such as an acid clay. The clay becomes spent, i.e., substantially incapable of further economic sorption of color bodies or of other economic use. (Such clay is also used as a catalyst to assist in polymerizing fatty acids to make "dimer" acids and higher polymers.)
Usually the spent clay is filtered off to yield a cake of about 25-65% clay solids laden with an oily residue of such acids. Disposal of such cake as landfill often conflicts with environmental considerations because of oil drainage and/or undesirable degradation of such residues. It represents also a waste of recoverable acids.
Heretofore, it has been proposed to wash spent clay catalyst vigorously with plain water in a prolonged operation for recovery of the clay (U.S. Pat. No. 3,873,585). Also, it has been proposed to wash spent bleaching clay from the bleaching of various oils, fats and waxes using sufficient aqueous soda ash or caustic soda solution to provide a fairly high pH (e.g., well above 7) in the aqueous phase of the clay washing operation for substantially neutralizing all fatty acids if any are present. Appreciable saponification of esters is experienced in some cases (U.S. Pat. Nos. 1,763,167; 1,078,435; 1,828,035; and 2,706,201). Collaterally the use of some alkali with crystalline clay catalyst in the preparation of polymeric fatty acids from unsaturated fatty acids has been proposed for reducing the ratio of trimer to dimer acids in the product (U.S. Pat. No. 2,955,121).
Advantages of the instant invention include reasonably rapid processing of the clay to obtain a high degree of fatty acid removal therefrom coupled with very modest use of alkali reagent, suppressing of excessive soap formation and attendant "tight" emulsion formation, and efficient recovery of fatty acid.